In this paper, some practical problems with the Message Authentication Codes (MACs), which are suggested in the current security architectures for wireless sensor network (WSN), are reconsidered. The analysis exploits the fact that the recommended MACs for WSN, e.g., TinySec (CBC-MAC), MiniSec (OCB-MAC), and SenSec (XCBC-MAC), are not exactly suitable for body sensor network (BSN). Particularly a dedicated attack is elaborated on the XCBC-MAC. Considering the hardware limitations of BSN, we propose a tunable lightweight MAC based on the PRESENT block cipher, which is named . A 128-bit variant is proposed for a higher resistance against internal collisions. Compared to the existing schemes, our lightweight MACs are time and resource efficient on hardware-constrained devices.